Science —

Chemical origami used to create a DNA Möbius strip

Researchers at Arizona State University have recently used origami to fold DNA into a Möbius strip. Why? Because its frickin' cool, that’s why. The scientists, who hail from the departments of biophysics, chemistry, and biochemistry, chose to make one out of DNA "not only because it is artistically inspiring, but also because it will likely display unique material properties that may be applied to create novel molecular devices."

A Möbius strip is a surface with only one side and only one boundary. To create one, they used single stranded M13mp 18 viral DNA as a scaffolding, and added 164 short pieces of DNA as staple strands attached to the scaffolding to help fold it into the desired structure. Each strip is roughly 210nM long, contains 61.5 helical turns, and is about 25-30nM wide, containing eleven DNA double helices and the gaps between them. There are 10.67 base pairs per helical turn. This very closely mimics the 10.5 pairs in B-type DNA, the form most commonly found in cells. They found an almost equal distribution of left- and right-handed chiralities in their strips, and concluded that the handedness is determined randomly. (DNA in biological systems is left-handed).

Atomic Force Micrograph of the DNA Möbius strips.

<em>Nature</em>, by permission of author H. Yan.

A neat feature of Möbius strips is that cutting them in different ways yields other topological structures. The scientists incorporated specific cutting sites into their DNA sequences, allowing DNA strand displacement to reconfigure the molecule. This is akin to the Japanese art of kirigami, which includes cutting of a folded paper.

Just like a Möbius strip made of paper, when this DNA Möbius strip is cut down the middle, it generates a loop half as narrow and twice as long as the original, with four half turns (a twist of 720o) around its middle axis. It is no longer a Möbius strip, as it now has two distinct surfaces and edges. By cutting along the length approximately one third of the way into the width, they created a catenene, otherwise known as two interlocking loops. They note that the only other way to connect two loops of DNA requires cutting one of them into a line, stringing it through the other, and then reconnecting its ends.

They hope that the combination of DNA self assembly (origami) and reconfiguration (kirigami) used here could be used to make more complex nanostructures that might be difficult to achieve by other methods, like knots and even shapes new to molecular engineering.